Plasma PLTP (phospholipid-transfer protein): an emerging role in 'reverse lipopolysaccharide transport' and innate immunity.

Plasma PLTP (phospholipid-transfer protein) is a member of the lipid transfer/LBP [LPS (lipopolysaccharide)-binding protein] family, which constitutes a superfamily of genes together with the short and long PLUNC (palate, lung and nasal epithelium clone) proteins. Although PLTP was studied initially for its involvement in the metabolism of HDL (high-density lipoproteins) and reverse cholesterol transport (i.e. the metabolic pathway through which cholesterol excess can be transported from peripheral tissues back to the liver for excretion in the bile), it displays a number of additional biological properties. In particular, PLTP can modulate the lipoprotein association and metabolism of LPS that are major components of Gram-negative bacteria. The delayed association of LPS with lipoproteins in PLTP-deficient mice results in a prolonged residence time, in a higher toxicity of LPS aggregates and in a significant increase in LPS-induced mortality as compared with wild-type mice. It suggests that PLTP may play a pivotal role in inflammation and innate immunity through its ability to accelerate the 'reverse LPS transport' pathway.